Analytical system with photonic crystal sensor

ABSTRACT

A system for determining whether interaction occurs between a trial substance and a target substance. The system includes a photonic crystal sensor having a photonic crystal structure and a defect member disposed adjacent the photonic crystal structure. The defect member defines an operative surface able to receive the target substance and the trial substance. The system further includes a light source that inputs a light signal to the photonic crystal structure and the defect member. The light signal is internally reflected, and a resultant output signal is outputted. The output signal relates to whether the trial substance interacts with the target substance at the operative surface. Furthermore, the system includes an identity detector that identifies the trial substance that interacts with the target substance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 11/881,040, filed Jul. 25, 2007, which claims the benefit of U.S. Provisional Application No. 60/833,101, filed on Jul. 25, 2006, the disclosures of which are incorporated herein by reference.

GOVERNMENT RIGHTS

This invention was made with government support under NIH Award No. 5 R21 RR021893-03. The government has certain rights in the invention.

FIELD

The present disclosure relates to an analytical system and, more particularly, relates to an analytical system with a photonic crystal sensor.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

Photonic crystals (PC) are periodic dielectric structures with a band gap forbidding propagation of a certain frequency range of light. It is understood that controlling photon modes by PC structures can be useful. For example, electromagnetic waves can be bent with high efficiency around 90-degree corners within radii smaller than a wavelength with two-dimensional (2D) PC structures. Furthermore, a 3D PC can be used to control the timing of light emitted by a quantum dot. Moreover, a dual core photonic crystal fiber can be used for enhancing two-photon fluorescence biosensing sensitivity.

Selection from various types of PCs depends on specific applications. For example, 3D PCs are used in order to control spontaneous emission. In the case of controlling laser beams which are close to plane waves, a 1D PC is sufficient and preferable due to its simplicity in fabrication. Additionally, 1D PCs are used in various applications, such as an omnidirectional reflector, low-threshold optical switching, and nonlinear optical diodes.

Furthermore, a technique has been developed for enhancing fluorescence by sandwiching the sample of interest (e.g., chromophores) between two pieces of 1D PCs. When a structural defect is introduced in the PCs, a photon-localized state can be created in the photonic band gap and the electric field around the defect member is enhanced. In one embodiment, two-photon fluorescence emission from 2-aminopurine in the PC structure was enhanced by a factor of 120. However, the application of this approach is limited because the thick substrate of the PC structure inhibits the sample from being observed with an optical microscope or from interacting with other biomolecules.

SUMMARY

A system for determining whether interaction occurs between a trial substance and a target substance is disclosed. The system includes a photonic crystal sensor having a photonic crystal structure and a defect member disposed adjacent the photonic crystal structure. The defect member defines an operative surface able to receive the target substance and the trial substance. The system further includes a light source that inputs a light signal to the photonic crystal structure and the defect member. The light signal is internally reflected, and a resultant output signal is outputted. The output signal relates to whether the trial substance interacts with the target substance at the operative surface. Furthermore, the system includes an identity detector that identifies the trial substance that interacts with the target substance.

Furthermore, a method of determining whether interaction occurs between a trial substance and a target substance is disclosed. The method includes delivering the target substance relative to an operative surface of a photonic crystal sensor. The photonic crystal sensor includes a photonic crystal structure and a defect member disposed adjacent the photonic crystal structure. The defect member defines the operative surface. The method further includes delivering the trial substance relative to the operative surface. Moreover, the method includes inputting an input light signal from a light source to the photonic crystal structure and the defect member such that the input light signal is internally reflected and such that an output signal is outputted. The method additionally includes detecting the output signal to determine whether the trial substance interacts with the target substance. Furthermore, the method includes identifying the trial substance that interacts with the target substance.

In addition, a system for determining whether a trial substance binds with a target substance is disclosed. The system includes a fluidics system having a common channel, a target branch that branches from the common channel, and a control branch that branches from the common channel. The system also includes a target photonic crystal sensor and a control photonic crystal sensor. Each of the target and control photonic crystal sensors include a respective photonic crystal structure and a respective defect member. The defect members define a respective operative surface. The target photonic crystal sensor is fluidly connected to the target branch, and the control photonic crystal sensor is fluidly connected to the control branch. Moreover, the fluidics system delivers the target substance relative to the operative surface of the target photonic crystal sensor and withholds the target substance from the operative surface of the control photonic crystal sensor. The fluidics system also delivers a plurality of different trial substances to the target and control photonic crystal sensors. Additionally, the system includes a light source that inputs a light signal to the photonic crystal structure of the target photonic crystal sensor. The light signal is internally reflected, and a resultant output signal is outputted. The output signal relates to whether any of the plurality of trial substances binds with the target substance. Furthermore, the system includes a target mass spectrometer that receives a downstream flow of the plurality of trial substances from the target photonic crystal sensor and that measures a change in an amount of the trial substances received over time. The system further includes a control mass spectrometer that receives a downstream flow of the plurality of trial substances from the control photonic crystal sensor and that measures a change in an amount of the trial substances received over time. The system additionally includes a controller with a processor that compares the change in amount of the trial substances received by the target mass spectrometer with the change in amount of the trial substances received by the control mass spectrometer in order to identify which of the plurality of trial substances binds with the target substance and to determine how long the identified trial substance binds with the target substance.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

FIG. 1 is cross sectional view of one embodiment of a photonic crystal (PC) sensor constructed according to the present disclosure;

FIG. 2 is a graphical comparison of fluorescence intensity from samples with and without a PC sensor of the type shown in FIG. 1;

FIG. 3A is a graph of a spectrum curve representing enhanced fluorescence from a PC sensor of the type shown in FIG. 1;

FIG. 3B is a graph of a decay curve representing enhanced fluorescence from a PC sensor of the type shown in FIG. 1;

FIG. 4A is a graph of a calculated light spectrum that passes through a PC sensor of the type shown in FIG. 1 without doping of an absorbing material;

FIG. 4B is a graph of a calculated light spectrum that passes through a PC sensor of the type shown in FIG. 1 doped with absorbing material;

FIG. 5 is a graph showing reflectance spectrum shift for PC sensors of the type shown in FIG. 1 when an adlayer is attached to the operative surface;

FIG. 6 is a graph showing that the intensity of a reflected light at a fixed wavelength changes if the reflectance spectrum shifts for PC sensors of the type shown in FIG. 1;

FIG. 7 is a graph showing a baseline shift comparison between SPR detection and PC detection;

FIG. 8 is a schematic diagram of a detection system employing a PC sensor of the type shown in FIG. 1;

FIG. 9 is a top view of a PC sensor for differential reflectance measurements;

FIG. 10 is a side view of another embodiment of a detection system employing a PC sensor with a defect member having an angled shape;

FIG. 11A is a graph showing experimental and calculated transmission spectra at normal incident direction for a PC sensor fabricated by an electron-beam evaporation method;

FIG. 11B is a graph showing experimental and calculated transmission spectra at normal incident direction for a PC sensor fabricated by a MBE method;

FIG. 12A is a graph showing a spectrum of a light source and a reflected light spectrum for a PC sensor;

FIG. 12B is a graph showing an experimental and simulated PC reflectance spectrum;

FIG. 13A is a graph showing a relationship between resonant wavelength and incident angle for a PC sensor;

FIG. 13B is a graph showing a relationship between resonant wavelength and solvent refractive index for a PC sensor;

FIG. 13C is a graph showing a relationship between resonant wavelength shift and adlayer thickness for a PC sensor;

FIG. 14 is a graph showing incident angle dependence of the reflectance for a PC sensor at a fixed wavelength;

FIG. 15 is a graph showing reflectance spectra of a PC sensor with and without an adlayer;

FIG. 16A is a graph showing a signal intensity for a PC sensor;

FIG. 16B is a graph showing a reference intensity for a PC sensor;

FIG. 16C is a graph showing a ratio between the signal and reference channels for a PC sensor;

FIG. 17 is a graph showing an intensity ratio change of a PC sensor;

FIG. 18 is a table showing a comparison between PC and SPR systems;

FIG. 19A is a cross sectional view of a prior art etalon ultrasound sensor;

FIG. 19B is a cross sectional view of a PC ultrasound sensor;

FIG. 20 is a schematic view of an exemplary embodiment of a system for detecting whether substances interact;

FIG. 21 is a schematic view of the system of FIG. 20 during operation;

FIG. 22 is an exemplary embodiment of a graph indicating interaction of substances in the system of FIGS. 20 and 21;

FIG. 23 is an exemplary embodiment of a graph identifying a trial substance in the system of FIGS. 20 and 21 that interacts with a target substance;

FIG. 24 is another schematic view of the system of FIG. 20;

FIG. 25 is an exemplary embodiment of a graph identifying a trial substance in the system of FIGS. 20 and 21 that does not interact with the target substance; and

FIG. 26 is an exemplary embodiment of a graph identifying a trial substance in the system of FIGS. 20 and 21 that temporarily interacts with a target substance.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

Referring initially to FIG. 1, one embodiment of a photonic crystal (PC) sensor 10 is illustrated. In the embodiment shown, the PC sensor 10 includes a PC structure 12, a defect member 14 (e.g., defect layer) disposed adjacent the PC structure 12 on one side, and a prism 16 disposed adjacent the PC structure 12 on an opposite side. The defect member 14 defines an operative surface 15. Also, a substrate 18 is interposed between the PC structure 12 and the prism 16. The input light has total internal reflection (TIR) at the sensor top surface. Owing to the TIR, an imaginary PC structure exists, which results in a unique open microcavity.

As will be discussed in greater detail below, only one PC is used in a total internal reflection (TIR) geometry instead of a prior art closed cavity with two pieces of PCs. Thus, the PC sensor 10 is open and exposed, and can be easily influenced by other molecules or signals to be detected. The reflection spectrum of the PC structure is extremely sensitive to changes in thickness of the defect member 14 and/or to the refractive index of biomolecules bound to the defect member 14. Thus, using the PC sensor 10 in this unique configuration opens up a wide range of applications and forms the basic detection mechanism for constructing highly sensitive sensors for various situations.

As shown, input light from a light source (not shown) is inputted to the prism 16, the input light passes through the prism 16, the substrate 18, the PC structure 12, and the defect member 14 if a resonance condition is satisfied in the defect member 14. Then, the input light is totally internally reflected at the operative surface 15. If a resonance condition is not satisfied in the defect member 14, the input light merely passes through the prism 16 and the substrate 18, while it gets highly reflected by the PC structure. A light signal is outputted from the PC sensor 10. As will be discussed in greater detail below, the output light signal is monitored in order to detect a condition at the operative surface 15. For instance, the PC sensor 10 can be used for biomolecular assay or as an ultrasonic sensor.

The PC structure 12 includes a plurality of alternating pairs of layers of different dielectric materials. In one embodiment, each dielectric material has a different refractive index. In one embodiment, there are seven alternating layers of silica and hafnia with the top layer (i.e., the layer on which the defect member 14 is provided) being hafnia. Also, in this embodiment, the substrate 18 is made of glass. Moreover, the defect member 14 is made of silica and has a thickness that is different than the thickness of any of the layers within the PC structure 12. In another embodiment, the defect member 14 includes a plurality of layers of different materials. In addition, the defect member 14 includes an absorbing material in one embodiment. It will be appreciated that the materials used to make the PC structure 12, the substrate 18, and/or the defect member 14 could be of any suitable type without departing from the scope of the present disclosure.

Furthermore, in one embodiment, the thickness of each dielectric layers in the PC structure 12 is determined according to the following considerations. It is assumed that the incident angle at the substrate layer 18 is θ_(i). The refraction angles in the substrate 18, the silica layers of the PC structure 12, the hafnia layers of the PC structure 12, and the defect member 14 are θ_(s), θ_(A), θ_(B), and θ_(X), respectively. Also, n_(s), n_(A), n_(B), and n_(X) are the refractive index of the substrate 18, the silica layers of the PC structure 12, the hafnia layers of the PC structure 12, and the defect member 14, respectively. Therefore: n_(s) sin θ_(s)=n_(A) sin θ_(A), n_(X) sin θ_(s)=n_(B) sin θ_(B), n_(S) sin θ_(s)=n_(x) sin θ_(X)  (1)

The thickness of the dielectric layers in the PC structure 12 satisfies the following relation:

$\begin{matrix} {{n_{A}d_{A}\cos\;\theta_{A}} = {{n_{B}d_{B}\cos\;\theta_{B}} = \frac{\lambda}{4}}} & (2) \end{matrix}$ where λ is the center wavelength of the photonic band gap, and d_(A) and d_(B) are the thickness for the silica layers and hafnia layers, respectively.

From Eqs. (1) and (2), we obtain,

$\begin{matrix} {{d_{A} = \frac{\lambda}{4\left( {n_{A}^{2} - {n_{S}^{2}\sin^{2}\theta_{S}}} \right)^{1/2}}},{d_{B} = \frac{\lambda}{4\left( {n_{B}^{2} - {n_{S}^{2}\sin^{2}\theta_{S}}} \right)^{1/2}}}} & (3) \end{matrix}$

In order to obtain local field enhancement in the defect member 14, the thickness of the defect member 14 satisfies the following resonant condition,

$\begin{matrix} {{{2n_{X}d_{X}\cos\;\theta_{X}} + {\alpha\;\frac{\lambda_{d}}{2\pi}}} = \frac{\lambda_{d}}{2}} & (4) \end{matrix}$ where α represents the Goos Hänchen phase shift, and λ_(d) is the wavelength of the photonic defect state, which should be within the photonic band gap. The factor of 2 in the first term on the left hand side of equation 4 is due to the fact that the light double passes the defect member due to the TIR. From Eqs. (1) and (4), we have,

$\begin{matrix} {d_{X} = \frac{\left( {\pi - \alpha} \right)\lambda_{d}}{4{\pi\left( {n_{X}^{2} - {n_{S}^{2}\sin^{2}\theta_{S}}} \right)}^{1/2}}} & (5) \end{matrix}$

For s-polarization of incident light, the Goos Hänchen phase shift is given by the following expression:

$\begin{matrix} \begin{matrix} {\alpha_{s} = {{- 2}\;{\tan^{- 1}\left( \frac{{n_{t}\left( {\frac{\sin^{2}\theta_{X}}{\sin^{2}\theta_{C}} - 1} \right)}^{1/2}}{n_{X}\cos\;\theta_{X}} \right)}}} \\ {= {{- 2}{\tan^{- 1}\left( \left( \frac{{n_{S}^{2}\sin^{2}\theta_{S}} - n_{t}^{2}}{n_{X}^{2} - {n_{S}^{2}\sin^{2}\theta_{S}}} \right)^{1/2} \right)}}} \end{matrix} & (6) \end{matrix}$ where n_(t) is the refractive index of the media on the defect member, and θ_(C) is the critical angle for the TIR. The thickness of the defect member 14 thus is determined according to:

$\begin{matrix} {d_{X} = {\frac{\lambda_{d}}{4{\pi\left( {n_{X}^{2} - {n_{S}^{2}\sin^{2}\theta_{S}}} \right)}^{1/2}}\left( {\pi + {2\;{\tan^{- 1}\left( \left( \frac{{n_{S}^{2}\sin^{2}\theta_{S}} - n_{t}^{2}}{n_{X}^{2} - {n_{S}^{2}\sin^{2}\theta_{S}}} \right)^{1/2} \right)}}} \right)}} & (7) \end{matrix}$

For p-polarization of incident light, the Goos Hänchen phase shift is given by the following expression:

$\begin{matrix} \begin{matrix} {\alpha_{p} = {{- 2}{\tan^{- 1}\left( {\frac{n_{X}}{n_{t}} \cdot \frac{\left( {\frac{\sin^{2}\theta_{X}}{\sin^{2}\theta_{C}} - 1} \right)^{1/2}}{\cos\;\theta_{X}}} \right)}}} \\ {= {{- 2}{\tan^{- 1}\left( {\left( \frac{n_{X}}{n_{t}} \right)^{2} \cdot \left( \frac{{n_{S}^{2}\sin^{2}\theta_{S}} - n_{t}^{2}}{n_{X}^{2} - {n_{S}^{2}\sin^{2}\theta_{S}}} \right)^{1/2}} \right)}}} \end{matrix} & (8) \end{matrix}$ The thickness of the defect member 14 for the p-polarization thus is determined according to:

$\begin{matrix} {d_{X} = {\frac{\lambda_{d}}{4{\pi\left( {n_{X}^{2} - {n_{S}^{2}\sin^{2}\theta_{S}}} \right)}^{1/2}}\left( {\pi + {2{\tan^{- 1}\left( {\left( \frac{n_{X}}{n_{t}} \right)^{2} \cdot \left( \frac{{n_{S}^{2}\sin^{2}\theta_{S}} - n_{t}^{2}}{n_{X}^{2} - {n_{S}^{2}\sin^{2}\theta_{S}}} \right)^{1/2}} \right)}}} \right)}} & (9) \end{matrix}$

In order to test fluorescence enhancement of the PC sensor 10, the center wavelength is chosen to be 600 nm. A 100 μL of 1 μM ethanol solution of Nile blue, a known dye molecule, is spin coated on the operative surface 15 of the defect member 14. A reference sample (not shown) is also constructed having a substrate deposited with only one silica layer. The same solution Nile blue solution is spin-coated on the reference sample. The reference sample and the PC sensor 10 are placed on a prism with index-matching fluid and excited by a laser output from an optical parametric amplifier tuned to 600 nm in wavelength. The emitted fluorescence is collected with a 20× objective lens and passes through a sharp-cut long-pass filter. A spectrometer coupled with a photon-counting streak scope is used to observe the wavelength- and time-resolved fluorescence.

The excitation power dependence of the fluorescence intensity is measured. In one embodiment represented in FIG. 2, a saturation of absorption occurs at approximately 0.24 mW excitation power for the PC sensor 10. Before the saturation, the observed fluorescence intensity from the PC sensor 10 was enhanced by 20-fold compared to that from the reference sample without a PC structure.

This result experimentally verifies that a single PC can be used in a TIR geometry to achieve local field enhancement. In addition, the fluorescence spectrum collected from top of the PC-TIR sample is not modified by the photonic band gap structure as represented in FIG. 3A. Also, the fluorescence decay curve shown in FIG. 3B has a decay constant of 2.3 ns, which is in agreement with the value of 2.6 ns for the reference sample within a margin of detection error. These results demonstrate that it is possible to form a microcavity by using only one piece of PC structure in a TIR geometry.

As will be discussed in greater detail below, the operative surface 15 of the defect member 14 is generally exposed so as be affected by external influences to be discussed. As such, the properties of the light reflected at the operative surface 15 will vary depending on the external influences at the operative surface 15. Thus, the output signal from the PC sensor 10 can be monitored for changes in order to detect the condition at the operative surface 15. Accordingly, the PC sensor 10 can be used for various sensing applications, such as kinetic analysis of biomolecular interactions or sensitive ultrasonic detections, and the like.

APPLICATION EXAMPLE 1 Biomolecular Assay

Specific interactions of biological molecules with various ligands, biopolymers, and membranes, such as protein:protein, protein:lipid, protein:DNA and protein:membrane binding, provide a chemical foundation for all cellular processes. The study of these biomolecular affinity and binding kinetics is of great importance for biomedical researches. For example, in order to discover a novel therapeutic antibody to treat cancer and other diseases, screening of a large repertoire of small molecules is necessary in order to identify high specificity and high affinity binders, followed by a more detailed characterization of the binding properties and determination of epitope specificity. Thus, there is an increasing demand for sensitive, accurate and high throughput analytical instruments that can provide insights on a molecular basis into critical biological processes.

One of the most widely used analytical techniques is based on surface plasmon resonance (SPR). In this known technique, a thin noble metal film is placed in an evanescent optical field, and the change of the SPR reports the binding of analytes to the ligand immobilized on the metal surface. Although this method allows label-free, real-time analysis, it has many drawbacks. For example, it is difficult to obtain accurate kinetic analysis due to the mass-transport limitation and it is not suitable for the measurement of small analytes (e.g., ˜1000 Da).

However, the PC sensor 10 of the present disclosure has a detection mechanism fundamentally different from the SPR and leads to a significant improvement in detection sensitivity. More specifically, the photonic defect state of the PC sensor 10 is extremely sensitive to the change in the thickness and/or refractive index of the defect member 14, and this characteristic is employed for a sensitive biomolecule analysis tool as described below.

In order to test this tool a PC sensor 10 is constructed that includes a PC structure 12 having three alternating layers of silica and titania disposed on a substrate 18, which is made of BK7 glass. The resonant wavelength is chosen to be 600 nm. The silica and titania layers of the PC structure 12 have a refractive index of 1.458 and 2.225, respectively, and the substrate 18 has a refractive index of 1.516. A defect member 14 with a refractive index of 1.49 is deposited on the top layer (titania) of the PC structure 12. The incident angle in the substrate 18 is chosen to be 68°. For s-polarization input light, the thickness of the silica, titania and the defect member 14 are 388.32 nm, 86.98 nm, and 446.32 nm, respectively, based on Eqs. (3) and (7), assuming the refractive index of the solution in contact with the defect member is 1.333. When the incident light wavelength falls in the photonic band gap, it is reflected by the PC structure 12 and does not reach the defect member 14. When the incident light wavelength matches the photonic defect state, the light reaches the defect member 14 and experiences TIR at the operative surface 15.

FIG. 4A shows the spectrum of light that reaches the defect member and experiences TIR when there is no absorption in the defect member. When the defect member 14 is doped with some absorbing material, the light is partially absorbed. In the calculation, we assume the extinction coefficient to be 0.0005 in the absorptive defect member 14, which corresponds to about only 0.32% absorption when there is no PC structure 12. FIG. 4B shows the corresponding spectrum in contrast to the case with an absence of absorption. The result shows that the absorption is more than 90%, enhanced by the PC structure 12 comparing 0.32% in the absence of a PC structure 12.

In practice, the portion of light reflected by the PC structure 12 and the portion reflected at the operative surface 15 are mixed and difficult to separate. Therefore, the total amount of the reflected light is used as a measurable quantity.

The defect member 14 is doped with absorbing materials, so that the reflected light that passes through the defect member has lower reflectance, thus resulting a reflectance dip at a specific wavelength corresponding to the defect state within the photonic band gap. When a thin layer is formed on the operative surface 15 (defined as an “adlayer” on the operative surface 15), the wavelength of the reflectance dip varies. It is appreciated that the adlayer could be formed by biological molecules to be observed in a biomolecular assay.

Then, the change in the output signal (i.e, the reflected light) from the PC sensor 10 is observed in order to detect the condition at the operative surface 15 due to the adlayer. More specifically, in one embodiment, a change in wavelength of the output light signal is detected as shown in FIG. 5 and/or a change in output signal light intensity at a wavelength of 632.8 nm is detected as shown in FIG. 6.

Specifically, a sharp and prominent dip appears in the reflection spectrum corresponding to the photonic defect state as shown in FIG. 5. This dip is relatively narrow and the resonant wavelength of this dip is sensitive to the material bound to the operative surface 15. For example, in the embodiment shown in FIG. 5, the dip width is only 0.1 nm and the resonant wavelength is shifted as much as 0.86 nm when the adlayer is 1 nm thick and with a refractive index of 1.46. This spectrum shift can be easily measured since the dip width is extremely narrow. Also, an even narrower dip width, and thus more sensitive detection, can be observed by increasing the incident angle and/or the number of alternating layers of the PC structure. It is noted that although the defect member 14 is absorptive, both immobilized reactants on the operative surface 15 and mobile reactants that form the adlayer need not be labeled. Thus, it is possible to obtain a label-free measurement for the sample of interest.

In addition to directly measuring the spectrum shift with a spectrometer, a differential reflectance measurement is employed at a fixed wavelength. FIG. 6 shows that the reflectance changes as much as 85.24% at the wavelength of a HeNe laser (632.8 nm), when a 0.1-nm thin adlayer with refractive index of 1.46 is formed on the sensor surface. Since a detection accuracy of 10⁻⁴˜10⁻⁵ can be obtained in a typical differential reflectance measurement, an extremely high detection sensitivity of molecular binding on the sensor surface can be achieved. The detectable adlayer thickness can be as small as 10⁻⁵˜10⁻⁶ nm. This is a significant improvement compared with the sensitivity of an SPR based instrument.

Besides higher detection sensitivity, the detection system using the PC sensor 10 has many other advantages over the SPR based detection, such as larger detection range, better baseline stability and flexible detection configurations. These advantages are described below.

Using the PC sensor 10, the adlayer is in the actual optical path of the input light signal, which increases the optical path length of the defect member 14. The reflectance dip of the photonic defect state shifts within the photonic bandgap of the PC structure 12 when the adlayer thickness and/or refractive index changes. The detection range is therefore restricted by the bandgap, which is around 700 nm for the PC structure 12 with three pairs of alternating dielectric layers and an incident angle of 68°. The detection range can be even wider by increasing the incident angle. In contrast, the detection range of an SPR instrument is limited to the range of the evanescent field, which is typically around 200 nm. Thus, the PC sensor 10 can be used to detect thicker adlayers or bigger particles compared to SPR measurements.

Also, for the detection range on the small side, a critical factor is the detection baseline stability. A small change in refractive index of the solution on the sensor surface may cause a resonant wavelength variation. There may be several causes for changes in the refractive index, such as the temperature. The evanescent field in SPR has a large portion (relative to the thin adlayer) in the bulk solution. The change in the refractive index of the solution contributes to the shift of SPR wavelength in the same way as the adlayer. A small change in the solution property results in nonnegligible fluctuation in the detection baseline. For example, when the refractive index of solution changes only by 0.0002, the SPR baseline drift is as large as 0.62 nm, which is equivalent to the change when a 0.25-nm adlayer with refractive index of 1.46 is attached to the defect member 14. On the other hand, the adlayer interacts with a propagating field in the PC sensor 10 and increases the actual optical path, while the contribution to the change in resonant wavelength from the solution is due to the Goos Hänchen phase shift, which is very small. Thus, the resonant wavelength is less affected by the solution. For the same change in the solution, the resonant wavelength of the PC sensor 10 shifts just 0.14 nm. FIG. 7 shows the comparison of baseline shift caused by very small fluctuations in the refractive index of bulk solution between SPR and PC-TIR detection.

In the SPR based measurements, the refractive index and thickness of the adlayer cannot be independently determined; one has to use the value of one of the parameters given by other measurements in order to calculate the value of the other parameter. In contrast, the refractive index and thickness of the adlayer can be independently determined using the PC sensor 10. The resonant wavelength shift of the defect state varies with the angle or polarization of the incident light, and this dependence is different for different refractive index of the adlayer. Thus, one obtains both the refractive index and adlayer thickness by carrying out the measurement with two different incident angles or two different polarizations.

Referring now to FIG. 8, one embodiment of a detection system 20 employing a PC sensor 10 is shown. In this embodiment, the detection system 20 is a bioassay system. The detection system 20 is modular because it includes a plurality of light sources 22 a, 22 b and a plurality of sensing devices 24 a, 24 b. In the embodiment shown, the detection system 20 can be used to detect spectral shift of the output signal and/or differential reflectance of the output signal.

Using the white light source 22 a, the reflectance spectrum is obtained using the PC sensor 10. A large detection range (about 1-700 nm) of adlayer thickness can be obtained. When the differential reflectance measurement is used, extremely high detection sensitivity can be achieved and the detectable range of the adlayer thickness is from 1 nm down to 10⁻⁵ nm.

In order to detect spectral shift, light from a broad band white light source 22 a is directed through a first lens 26 and is coupled into a single-mode (SM) fiber 28 to get a good optical mode, and the output beam from the fiber 28 is collimated with a second lens 30. The light from the white light source 22 a is then reflected by a first reflecting mirror 32 and through a linear polarizer 34 to adjust the light polarization. The light is reflected by a second reflecting mirror 36 that is mounted on a rotator 38. The position of the rotator 38 is controlled by a computer to adjust the incident angle. The light is then reflected again by a third reflecting mirror 40. The light enters the PC sensor 10 through the prism 16, is totally internally reflected at the operative surface 15 for the wavelength component that satisfies the resonance condition, or is reflected by the PC structure 12 for the other wavelength components. The total output signal from the PC sensor 10 is reflected by a fourth reflecting mirror 42, passes through a third lens 44, and is directed into a spectrometer sensing device 24 a. Thus, the spectral shift of the output signal can be detected.

To detect differential reflectance with the detection system 20, a laser 22 b is used as the light source. In one embodiment, the laser 22 b is a HeNe laser 22 b with the wavelength of 632.8 nm. Also, the PC sensor 10 includes a two-part structure represented in FIG. 9. On a first portion 50 of the operative surface 15, molecular binding occurs and an adlayer 51 is formed thereon. A second portion 52 of the operative surface 15 remains unchanged. As shown in FIG. 8, the laser beam passes through a fourth lens 54, through a pinhole 56, through a fifth lens 58, and through a diaphragm 60. Then, the laser beam is split into two by a splitter 62. One of the split beams is reflected by a fifth reflecting mirror 64, through the polarizer 34, and is reflected by the second and third reflecting mirrors 36, 40 to thereby illuminate the first portion 50 of the operative surface 15 having the adlayer 51. The other of the split beams is reflected by a sixth and seventh reflecting mirror 68, 66, through the polarizer 34, and is reflected by the second and third reflecting mirrors 36, 40 to thereby be directed at the second portion 52 of the operative surface 15 as a reference. The intensities of the two reflected beams are monitored by a second sensing device 24 b having two identical detectors. The intensity ratio between the two beams is recorded, which sensitively reflects the property of the adlayer 51.

Referring now to FIG. 10, another embodiment of a detection system 21 is illustrated. In this embodiment, the PC sensor 10 includes a defect member 14 having an operative surface 15 that is angled. More specifically, the operative surface 15 is angled so as to define a plane that intersects a plane defined by an opposite side 81 of the defect member 14.

The position where TIR occurs is observed. As shown, for a fixed incident angle and certain wavelength of incident light, the TIR occurs at a position where the defect member 14 thickness satisfies the resonance condition. Thus, by monitoring the position of TIR one can use the PC sensor 10 to detect if there is something (e.g. biomolecules) bound to the defect member 14 or if there is some signal that changes the thickness of the defect member 14.

Two techniques can be used to fabricate the PC sensor 10 for use in the detection system 20 shown in FIG. 8. First, electron-beam evaporation can be used. Silica, Titania and pure silicon are used as the target materials. Rutherford backscattering spectroscopy (RBS) is used to calibrate the thickness of deposited layers. The transmission spectrum of PC structure 12 and defect member 14 composed of silicon and silica at normal incident direction is measured, which is in agreement with simulation results as shown in FIG. 11A. Second, fifteen pairs of GaAs/AlAs layers are grown on a GaAs substrate 18 by MBE with high accuracy (˜0.1 nm). InxGa1-xAs (x=0.4) is used as the absorptive layer and its thickness (d=8 nm) is decided by considering both resonant dip depth and growing mismatch with GaAs. Another GaAs layer is added on top of InxGa1-x As to satisfy the resonant condition in the defect member. FIG. 11B shows the measured and calculated transmission spectrum at normal incident direction. The good agreement between the theoretical calculation and experimental result indicate that the PC sensor 10 is well fabricated.

In one embodiment, the PC sensor 10 is made by electron-beam evaporation. The thickness of the three pairs of Silica and Titania alternating layers in the PC structure 12 is 438 nm and 87 nm, respectively. Its defect member 14 is composed of 18-nm Silicon and 140-nm Silica.

FIG. 12A shows the light intensity of a broad band white light source reflected from the PC sensor 10 (as indicated by the curve 60) and a reference substrate (as indicated by the curve 62) used in a total internal geometry. FIG. 12B shows the experimental and simulated PC-TIR reflectance spectrum. In the calculation, the thickness of different layers are taken from the measured values, and the refractive indices of the substrate 18 (e.g., BK7), Silica and titania are 1.516, 1.458 and 2.225, respectively, at the wavelength of 600 nm. The refractive index and extinction coefficient of silicon are 3.94 and 0.0183 at 600 nm, respectively. The solvent used on the operative surface 15 is de-ionized (DI) water with a refractive index of 1.333. The incident angle is 64.5°. Both the simulation and experimental results show a primary resonance dip at 580 nm with a narrow width of 8 nm. The dip width is much narrower than that of a typical SPR resonance spectrum width (40 nm).

Accordingly, the resonant wavelength shifts to longer wavelength with decreasing the incident angle as shown in FIG. 13A. In addition, the dependence of the resonance wavelength on solvents is measured as shown in FIG. 13B. The resonant wavelength shift is only 150 nm per RIU for the solvent with a refractive index close to water. This small shift is preferred in order to have a system with high stability because a small temperature fluctuation may cause the change in solvent refractive index. The refractive index of water is known to decrease by ˜8×10⁻⁵ RIU per degree K near room temperature. Using the solvent refractive index dependence of the resonance wavelength shift 150 nm/RIU, the temperature stability of the PC-TIR system is −0.012 nm/K, which is remarkably improved comparing with that of an SPR system (i.e., −0.25 nm/K). The dependence of the resonant wavelength shift on the adlayer properties is also shown in FIG. 13C. As shown, the resonant wavelength sensitively shifts to longer wavelength with increasing the adlayer thickness.

In addition, the resonance dip is measured as a function of the incident angle for a fixed wavelength of 580 nm as shown in FIG. 14. The full width at half maximum is only 0.4°, which is about five times smaller than that in an SPR system. The experimental result is again in a good agreement with a simulation.

The PC sensor 10 also has an extremely high sensitivity in the differential reflectance measurement. Detection of a thin monolayer of small molecules can be carried out. For instance, the PC sensor 10 is first exposed to 5% APTES solutions for 20 minutes, then rinsed with de-ionized (DI) water and methanol and dried with nitrogen. After the silanization, the PC sensor 10 is exposed to a 2.5% glutaraldehyde solution in 20 mM HEPES buffer (pH=7.4) for 30 minutes, then rinsed with DI water and dried with nitrogen. A thin layer of Glutaraldehyde molecules are obtained due to its reaction with the amino groups on the silanized surface. The total thickness of the APTES/glutaraldehyde layer is 1.5 nm.

A resonance dip shift by 1.24 nm is observed in the reflectance spectrum measurement as shown in FIG. 15, when the APTES/glutaraldehyde adlayer is formed. In order to achieve higher sensitivity, differential reflectance measurements with a HeNe laser are used.

The intensity stability of the HeNe laser is measured to be about 2% as shown in FIGS. 16A and 16B. A clear improvement of the detection accuracy is obtained by measuring the intensity ratio between these two beams. The fluctuation of the ratio is less than 1.6*10⁻⁴ as shown in FIG. 16C.

Furthermore, a clear ratio change from 0.8232 to 0.7141 is observed (FIG. 17) when the thin APTES/glutaraldehyde adlayer is formed on the PC sensor 10.

The detection sensitivity of the sensor is expressed as,

${Sensitivity} = {{Adlayer}\mspace{14mu}{Thickness} \times \frac{{Detection}\mspace{14mu}{Accuracy}}{{Ratio}\mspace{14mu}{Change}}}$

Since the system has detection accuracy up to 1.6×10⁻⁴, and the ratio change is 0.1091 for a 1.5 nm adlayer, the detection sensitivity of the PC sensor 10 is 0.002 nm, which is significantly improved compared with the sensitivity of an SPR based instrument.

The theoretical detection limit is calculated using our simulation results. For a PC sensor 10 with three alternating layers in the PC structure 12, the resonance dip width is calculated to be 2 nm. A detection limit of 1.5×10⁻⁵ nm can be predicted for a PC sensor 10, which is in contrast to 3×10⁻³ nm for an SPR system. A comparison between the PC sensor 10 and SPR systems is shown in FIG. 18.

Thus, the PC sensor 10 offers the ability to perform real-time and label-free quantitative detections, allowing for a wide range of biomolecular assays with a higher sensitivity and better stability compared to known SPR-based instruments. In addition, the PC sensor 10 can independently determine the refractive index and thickness of the adlayer.

Referring now to FIG. 20, a further embodiment of a system 70 is illustrated that incorporates a PC sensor 10 a of the types discussed above. The system 70 can be used for determining whether interaction occurs between different substances. For instance, the system 70 can be used for performing a bioassay and determining whether biological substances bind together. Also, in some embodiments, the system 70 can be used to determine how long the substances bind together, whether the substances bind directly or indirectly to each other, and/or other characteristics of the substances as will be discussed in greater detail below.

As shown schematically in FIG. 20, the system 70 can include a delivery system 72. The delivery system 72 can be of any suitable type, such as a fluidics system (e.g., a micro-fluidics system) that includes one or more channels 73 capable of directing a fluid flow therethrough.

The system 70 can also include a PC sensor 10 a. The PC sensor 10 a included in the system 70 can be a PC sensor 10 a of any of the embodiments discussed above. As such, the PC sensor 10 a can include a photonic crystal structure 12 and a defect member 14 that defines an operative surface 15. The PC sensor 10 a can be in operative communication with the delivery system 72 in any suitable fashion. For instance, the operative surface 15 can be exposed to or within the channel 73 of the delivery system 72. As such, the operative surface 15 can receive a target substance 78 via the delivery system 72 as will be discussed in greater detail below. The operative surface 15 can also receive one or more trial substances 80 a-80 e via the delivery system 72. For instance, the trial substances 80 a-80 e can flow through the channel 73 toward the PC sensor 10 a after the target substance 78 has been delivered to the PC sensor 10 a. As such, the trial substances 80 a-80 e can have an opportunity to interact (e.g., bind) with the target substance 78 on the operative surface 15 of the PC sensor 10 a.

It will be appreciated that the target substance 78 and the trial substances 80 a-80 e can be of any suitable type, such as molecules of a protein, etc. Also, it will be appreciated that the delivery system 72 can deliver any suitable amount and concentration of the target and trial substances 78, 80 a-80 e.

Moreover, the system 70 can include a light source 75, such as a laser or other suitable light source 75. As discussed above, the light source 75 can input an input light signal 91 to the PC sensor 10 a, the light signal can be internally reflected in the PC sensor 10 a, and a resultant output light signal 93 can be outputted. It will be appreciated that, in some embodiments, only a small fraction of the input light signal 91 (e.g., within a relatively small wavelength range) experiences total internal reflection while the remaining portions of the input light signal 91 is reflected by the PC sensor 10 a. Thus, as discussed in detail above, characteristics of the output light signal 93 can relate to and can be dependent on whether any of the trial substances 80 a-80 e interacts with the target substance 78 at the operative surface 15.

Thus, the PC sensor 10 a can be used to detect whether binding occurs between any of the trial substances 80 a-80 e and the target substance 78. For purposes of clarity, the system 70 will hereafter be described as detecting whether binding occurs between any of the trial substances 80 a-80 e and the target substance 78; however, it will be appreciated that the PC sensor 10 a can be used to detect any other suitable interaction between the target and trial substances 78, 80 a-80 e.

Furthermore, the system 70 can include an identity detector 74 a that identifies the trial substances 80 a-80 e that bind with the target substance 78. For instance, the identity detector 74 a can be a commercially available mass spectrometer 76. However, it will be appreciated that the identity detector 74 a could be of any other suitable type, such as a nuclear magnetic resonance (NMR) device, an enzyme-linked immunosorbent assay (ELISA) device, etc. The identity detector 74 a can be fluidly connected to the delivery system 72. For instance, the identity detector 74 a can be located downstream of the PC sensor 10 a and can receive a downstream flow from the PC sensor 10 a via the delivery system 72. Accordingly, one or more of the trial substances 80 a-80 e (and, in some cases, the target substance 78) can flow from the PC sensor 10 a to be received by the identity detector 74 a. As will be discussed, the identity detector 74 a can analyze this flow from the PC sensor 10 a to identify and distinguish which of the trial substances 80 a-80 e binds with the target substance 78.

In addition, the system 70 can include a controller 77. The controller 77 can be of any suitable type, such as a computerized tool, that is in communication with both the PC sensor 10 a and the identity detector 74 a. Also, the controller 77 can include a processor 79 for processing data received from both the PC sensor 10 a and the identity detector 74 a. The controller 77 can also include a display (such as a computer monitor, printer, etc.) for displaying the processed results. Moreover, the controller 77 can control flow through the delivery system 72 as will be discussed in greater detail below.

FIG. 24 further illustrates various embodiments of the system 70. As shown, the system can include a plurality of PC sensors, namely, a target PC sensor 10 a and a control PC sensor 10 b. Also, the system 70 can include a target identity detector 74 a and a control identity detector 74 b. The delivery system 72 can include a common channel 86. The delivery system 72 can further include a first branch 88 and a second branch 90 that are each downstream of the common channel 86 and that each fluidly branch off of the common channel 86. The first branch 88 can fluidly connect the target PC sensor 10 a to the common channel 86 and the target PC sensor 10 a to the target identity detector 74 a. Also, the second branch 90 can fluidly connect the control PC sensor 10 b to the common channel 86 and the control PC sensor 10 b to the control identity detector 74 b. Also, the system 70 can include a valve 92 that controls fluid flow through the first and second branches 88, 90 as will be discussed. Furthermore, as shown in FIG. 24, the controller 77 can be in communication with both the target and control PC sensors 10 a, 10 b and both the target and control identity detectors 74 a, 74 b. (It will be appreciated that FIGS. 20 and 21 illustrate the first branch 88, the target PC sensor 10 a, and the target identity detector 74 a.)

During use of the system 70, the controller 77 can control the valve 92 such that the first branch 88 is open and the second branch 90 is closed. Then, the controller 77 can cause the target substance 78 to flow through the first branch 88 to the target PC sensor 10 a to be deposited on the operative surface 15 of the target PC sensor 10 a. For instance, the target substance 78 can be included at a known concentration within an appropriate coating buffer solution. It will be appreciated that target substance 78 will be deposited on the operative surface 15 of the target PC sensor 10 a, but the target substance 78 will not be deposited the control PC sensor 10 b.

Subsequently, the controller 77 can control the valve 92 such that both the first and second branches 88, 90 are open, and the controller 77 can cause the trial substances 80 a-80 e to flow through the first and second branches 88, 90 toward each of the target and control PC sensors 10 a, 10 b. For instance, the trial substances 80 a-80 e can be included at a known concentration as an analyte within a running buffer solution.

As shown in FIG. 21, some of the trial substances 80 a, 80 b, 80 c may bind to the target substance 78 on the target PC 10 a while other trial substances 80 d, 80 e may flow freely away from the target substance 78. For instance, trial substances 80 a, 80 c can bind directly to the target substance 78. Also, trial substance 80 b can bind directly to trial substance 80 a to indirectly bind to the target substance 78. It will be appreciated that some of the trial substances 80 a, 80 b, 80 c may bind temporarily (directly or indirectly) to the target substance 78 and then subsequently release to flow toward the identity detector 74 a. As discussed above, the light source 75 can emit light in order to detect whether binding is occurring at the operative surface 15. It will be appreciated that the PC sensor 10 a can be used to detect whether binding is occurring in real time. Also, the PC sensor 10 a can be used to detect whether binding is occurring using relatively low concentrations of the target and trial substances 78, 80 a-80 e.

The controller 77 can receive data from the PC sensor 10 a and can compile the received data into any suitable form, such as the exemplary graph illustrated in FIG. 22. As shown, the controller 77 can plot the intensity of the output light signal 93 from the PC sensor 10 a versus time. As shown in the exemplary embodiment in FIG. 22, the intensity increases substantially at times t₁, t₂ and t₃. For instance, this can indicate that trial substance 80 a binds at time t₁, trial substance 80 b binds at time t₂, and trial substance 80 c binds at time t₃.

The target identity detector 74 a can receive the downstream flow from the target PC sensor 10 and can identify each of the substances contained therein. Also, the control identity detector 74 b can receive the flow through the second branch 90 and can identify each of the substances contained therein. The identity detectors 74 a, 74 b can be used to detect the concentrations or amounts of the trial substances 80 a-80 e received over time. The controller 77 can compare the results of the target and control identity detectors 74 a, 74 b.

More specifically, the controller 77 can receive data from the target and control identity detectors 74 a, 74 b and can compile the received data into any suitable form, such as one or more graphs of the type shown in FIGS. 23 and 25. As shown in FIG. 23, the controller 77 can plot the change in concentration of the trial substance 80 a received by the target identity detector 74 a over time as shown by line 97 a. Also, the controller 77 can plot the change in concentration of the trial substance 80 a received by the control identity detector 74 b over time as shown by line 99 a. Then, by subtracting the target data (point T) from the control data (point C) at a specific time t_(n), the amount of the trial substance 80 a at time t_(n) can be detected.

Also, as shown in FIG. 25, a similar graph can be generated for trial substance 80 d. It will be appreciated that a separate graph can be generated for each of the trial substances 80 a-80 e.

Moreover, the controller 77 can compare the data from the target PC sensor 10 a to the data from the identity detectors 74 a, 74 b in order to detect which of the trial substances 80 a-80 e are binding to the target substance 78 and which of the trial substances 80 a-80 e are not. More specifically, the target identity detector 74 a can determine a time t₁ when binding is occurring on the target identity detector 74 a as discussed above and as shown in FIG. 22. Then, the amount of each substance 80 a-80 e approximately at time t₁ can be detected (t_(n)≈t₁) using the data generated by the target and control identity detectors 74 a, 74 b. For instance, if time t_(n) in FIGS. 23 and 25 is approximately equal to time t₁, the amount of trial substance 80 a is relatively low, and the amount of trial substance 80 d is relatively high. Thus, it can be reasonably assumed that substance 80 a is binding with the target substance 78 while substance 80 d is not binding with the target substance 78. A similar analysis can be performed for each of the target substances 80 a-80 e for time t₁. Furthermore, a similar analysis can be performed for each of times t₁, t₂ and t₃.

Moreover, it will be appreciated that the system 70 can be used to determine how long the trial substances 80 a-80 e bind with the target substance 78. More specifically, as shown in FIG. 26, the identity detector 74 a can detect that the received amount of trial substance 80 b is relatively low at or near time t_(n), and the amount of trial substance 80 b is substantially higher at time t_(n+1). Thus, it can be reasonably assumed that substance 80 b binds for a time approximately equal to t_(n+1) minus t_(n).

Subsequently, a regenerate buffer solution can be delivered through the first and second branches 88, 90 of the delivery system 72 to clean the operative surface 15 of the PC sensor 10 a. As such, the trial substances 80 a-80 e and the target substance 78 can be removed from the PC sensor 10 a. The analyses discussed above can be performed in conjunction with the delivery of the regenerate buffer solution.

Furthermore, in some embodiments, a wash buffer solution can be delivered through the first and second branches 88, 90. The wash buffer can be different than the buffer used when the trial substances 80 a-80 e were previously delivered. For instance, the wash buffer can have a different concentration of salts. As such, the wash buffer can remove those trial substances 80 a-80 e that are weakly bound to the target substance 78. Thus, by performing the tests described above in combination with a plurality of wash buffer solutions, the strength of binding of the trial substances 80 a-80 e with the target substance 78 can be tested.

In addition, a plurality of tests can be performed to determine if the trial substances 78, 80 a-80 e are binding directly or indirectly to the target substance 78. For instance, the trial substance 80 a and the trial substance 80 b can be tested, and binding of both trial substances 80 a, 80 b will likely be detected. Subsequently, the trial substance 80 b can be tested alone, and binding is unlikely to be detected. Thus, it can be reasonable to assume that trial substance 80 b directly binds to the trial substance 80 a and the trial substance 80 b indirectly binds to the target substance 78 (see FIG. 21).

Accordingly, the system 70 can be used for accurate, real time analysis of the interaction of the target and trial substances 78, 80 a-80 e. Furthermore, the system 70 can be used for label-free analysis of these interactions. Moreover, the system 70 can be used to detect interactions at relatively low concentrations of the target and trial substances 78, 80 a-80 e.

APPLICATION EXAMPLE 2 Ultrasonic Detector

The PC sensor 10 can also be employed in an ultrasonic detector. Specifically, the exposed operative surface 15 enables use of the PC sensor 10 as an ultrasonic detector. Optical detection of ultrasound by using an etalon has been demonstrated as shown in FIG. 19A. As shown, the incident and reflected optical signals are presented as spatially separate but, in practice, are collinear. Acoustic displacement at the etalon surface changes the cavity length, which in turn changes the intensity of the optical signal reflected from the etalon. However, the closed structure of the etalon limits the detection sensitivity.

On the other hand, by using the PC sensor 10, the etalon cavity is opened so that the sensor interface can directly interact with the ultrasonic signals. As such, a material with large elasticity can be used as the defect member 14, which is difficult to use in a closed etalon cavity because the two high reflection surfaces are intended to remain parallel to each other and flat. Thus, larger change of the optical response to an ultrasonic signal can be obtained compared with prior art detection using an etalon. In addition, the PC sensor 10 has advantages in optical generation of ultrasound. Because the optical field is enhanced at the operative surface 15 of the defect member 14 of the PC sensor 10, the ultrasonic signal is generated and propagates directly from the operative surface 15 without attenuation by any other additional layers, thus allowing strong ultrasound generations. The PC sensor 10 therefore makes it possible to integrate a strong optical ultrasound generator with a sensitive optoacoustic receiver.

The invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described. 

What is claimed is:
 1. A system for determining whether interaction occurs between a trial substance and a target substance, the system comprising: a photonic crystal sensor having a photonic crystal structure and a defect member disposed adjacent the photonic crystal structure, the defect member defining an operative surface able to receive the target substance and the trial substance, the photonic crystal sensor operable to receive an input light signal that is internally reflected at the operative surface and that produces a resonance reflectance dip in a resultant output light signal, the resonance reflectance dip being indicative of at least one of scattering and absorption of the input light signal; a light source that inputs the input light signal to the photonic crystal structure and the defect member; an output light sensor that receives the output light signal and that detects the resonance reflectance dip therein to detect whether interaction occurs between the trial substance and the target substance; an identity detector that identifies the trial substance that interacts with the target substance, and a delivery system, a processor, a target photonic crystal sensor, and a control photonic crystal sensor, wherein: each of the target and control photonic crystal sensors include a respective one of the photonic crystal structure and the defect member, the delivery system delivers the target substance to the target photonic crystal sensor and withholds delivery of the target substance to the control photonic crystal sensor, the delivery system delivers the trial substance to each of the target and control photonic crystal sensors, the delivery system delivers a downstream flow from the target photonic crystal sensor and a downstream flow from the control photonic crystal sensor, and the processor compares an amount of the trial substance in the downstream flow from the target photonic crystal sensor to an amount of the trial substance in the downstream flow from the control photonic crystal sensor.
 2. The system of claim 1, wherein the delivery system includes a fluidic system with a common channel, a first branch off of the common channel, and a second branch off of the common channel, the first branch fluidly connecting the target photonic crystal sensor and the common channel, and the second branch fluidly connecting the control photonic crystal sensor and the common channel.
 3. The system of claim 2, further comprising a valve that controls fluid flow through at least one of the first and second branches.
 4. The system of claim 1, wherein the identity detector includes an enzyme-linked immunosorbent assay device.
 5. A system for determining whether a trial substance binds with a target substance, the system comprising: a fluidics system having a common channel, a target branch that branches from the common channel, and a control branch that branches from the common channel; a target photonic crystal sensor and a control photonic crystal sensor, each of the target and control photonic crystal sensors including a respective photonic crystal structure and a respective defect member, the defect members defining a respective operative surface, the target photonic crystal sensor operable to receive an input light signal that is internally reflected at the respective operative surface and that produces a resonance reflectance dip in a resultant output light signal, the resonance reflectance dip being indicative of at least one of scattering and absorption of the input light signal, the target photonic crystal sensor being fluidly connected to the target branch, the control photonic crystal sensor being fluidly connected to the control branch, the fluidics system delivering the target substance relative to the operative surface of the target photonic crystal sensor and withholding the target substance from the operative surface of the control photonic crystal sensor, the fluidics system also delivering a plurality of different trial substances to the target and control photonic crystal sensors; a light source that inputs the light signal to the photonic crystal structure of the target photonic crystal sensor; an output light sensor that receives the output light signal and that detects the resonance reflectance dip therein to detect whether binding occurs between the trial substance and the target substance; and a target mass spectrometer that receives a downstream flow of the plurality of trial substances from the target photonic crystal sensor and that measures a change in an amount of the trial substances received over time; a control mass spectrometer that receives a downstream flow of the plurality of trial substances from the control photonic crystal sensor and that measures a change in an amount of the trial substances received over time; and a controller with a processor that compares the change in amount of the trial substances received by the target mass spectrometer with the change in amount of the trial substances received by the control mass spectrometer in order to identify which of the plurality of trial substances binds with the target substance and to determine how long the identified trial substance binds with the target substance. 